Design of fail-safe controller for brake-by-wire systems using optimal braking force distribution

In this paper, a method for mitigating the risk of potential brake actuator failure during braking in vehicles with BBW(Brake-By-Wire) systems is described. When the failure of one brake actuator occures during braking, the vehicle cannot stop as quickly as driver wants and the vehicle may fishtail because of imbalance braking force. To avoid this dangerous situation, a novel fail-safe control algorithm is proposed. The proposed fail-safe control algorithm consists of 2 steps. In the first step, corrective yaw moment is determined to manage the undesired yaw moment caused by asymmetric braking. In the second step, the additional braking forces are re-distributed to normally remaining actuators using optimal design methods such as Lagrange multiplier and KKT (Karush-Kuhn-Tucker) condition. The simulation results demonstrate that the proposed control algorithm can make the vehicle with a failed brake actuator follow the desired deceleration more closely and achieve the remarkable reduction in undesired yaw moment. To validate the proposed fail-safe controller, simulations on the well-known vehicle simulation software, Carsim, were conducted.